Heaters using conductive woven tapes



May 3l, 1960 R. E. CRUMP HEATERS USING coNDucTIvE wovEN TAPES FiledApril 18, 195s r' l| f| ufl rroeA/Exs.

United States Patent O HEATERS USING CONDUCTIVE WOVEN TAPES Ralph E.Crump, Granada Hills, Calif., assignor to Electrolilm, Inc., NorthHollywood, Calif., a corporation of California Filed Apr. 18, 1958, Ser.No. 729,297

9 Claims. (Cl. 219-4'6) This invention relates to improved kelectricheating units which are in certain respects improvements on the typeofheating element disclosed and claimed in copending applications SerialNo.` 596,064, led July 5, 1956, now abandoned, by Arthur N. Heath onSheet Or Layer Form Heating Elements, and Serial No. 644,070 filed March5, 1957, now Patent No. 2,884,509, by Arthur N. Heath on Heating ElementContaining a Conductive Mesh.

In the above mentioned applications, there has been disclosed a uniquetype of electric heater unit in which the electrically resistive heaterelement takes the form of a closely woven mesh. At least some of thestrands forming this mesh are of electrically conductive material, andoffer sufficient resistance to develop heat when current is passedthrough the mesh. Preferably, the heater unit includes a layerofnon-conductive material, such as a suitable resinous plastic materialreinforced by and irnpregnating a sheet of cloth, and bonded to one sideof thev woven mesh to hold the various strands of the mesh in fixedrelative positions, and to insulate the mesh. For best results, and toprovide an ultimate product of maximum usefulness, two such insulativelayers are provided at the two opposite sides respectively of the mesh.

The general object `of the present invention is to provide a heater ofthe above discussed type which is especially designed so that itsmesh-form heater element may be manufactured continuously as anelongated'thin tape or strip of material, which can then be cut to anydesired length and be applied with maximum facility to any of numerousdifferent uses. Particularly contemplated is a tape of this type whichisso constructed that, after it has been cut to a desired length, bothof the power leads to the `tape can be connected to the same end of thetape. This feature has proven in practice to be of very greatimportance, since in many of the situations in which the present type ofheater can be used, the two ends of the tape 'must necessarily beseparated a substantial distance from one another, so that it becomesvery inconvenient to connect the power lead's `to these two differentends of the tape. Y

In order to allow connection ofk the two power leads to a common end ofthe tape, l so form the tape as to have two conductive areas extendinglongitudinally along the tape, withk a non-conductive area of the tapevextending longitudinally between the two conductive areas. In forming aheater unit from this tape, the two power leads are connected to the twoconductive areas at a rst end of the tape, and these two areas areelectrically connected together at the other end,` so that current owsrst in one direction along a first of the conductive areas and then in areverse direction along the other area.

The tape includes some non-conductive strands', typically iiber glass,in addition to the conductive strands. These non-conductive strands formthe non-conductive intermediate area of the tape, and also may be woventhrough the `two conductive areas to assist in holding the conductors inaccurately predetermined relation duringY "ice manufacture, and to thusgive the tape an accurately predeterminable and controlled resistancecharacteristic; The conductors may in some cases extend onlylongitudinally of the tape, but for optimum results they preferably alsoextend transversely of the tape, at the con'- ductive areas, so that thetransverse strands can function as potential equalizers for conductingequalizing current transversely between corresponding portions ofdifferent longitudinal conductors. This potential equalizing function isparticularly useful if one of the conductor circuits becomes damaged andpartially opened at one location, in which case the transverseconductors allow a transverse flow of current as necessary to allow thecurrent to pass the damaged location. l

The power connections to the conductive tape, and the cross connectionbetween the two conductive areas, may be formed by bus elements engagingthe conductors of the tape, and each confined between the tape and oneof the insulative outer layers.` These bus elements may take the form ofthin metal bus bars or screens lying against the tape at the desiredterminal locations, to contact the tape conditions over an extendedarea.

The above and other features and objects of the present invention willbe better understood from the following detailed description of thetypical embodiments illustrated in the accompanying drawing, in which:

Fig. l is a plan view of a first form of heater unit constructed inaccordance with the invention;

Fig. 2 is an enlarged fragmentary section taken on line 2-2 of Fig. l;

Fig. 3 is a greatly enlarged fragmentary section taken on line 3-3 ofFig. 4, and showing only the woven mesh portion of the unit, without theinsulative layers;

Fig. 4 is an enlarged fragmentary plan view of the woven mesh of Fig. l;i I

Fig. 5 is a view corresponding to Fig. 1, but showing a variational formof the invention;

Fig. 6 is a section taken on line 6 6 of Fig. 5.

Fig. 7 is an enlarged fragmentary plan view of the woven mesh in anothervariational arrangement.

Referring iirst to Figs. l to 4, the heater unit 10 shown in those gurestakes the form of a thin laminated composite sheet-like unit, typicallyapplied to the surface of a carrier member 11. This carrier member maybe any of a wide variety of types of parts, which it is desired to heat,or to radiate heat from, as for instance an aircraft part which is to beheated to prevent icing, an electronic component or device which is tobe heated to render it unsusceptible to ambient temperaturefluctuations, or a pipe or tube carrying a chemical which should notlose its heat (e.g., liquid sodium). 1n the Fig.`l form of theinvention, it may be assumed that the unit 10 is bonded directly tocarrier part 11, and this carrier part may be either rigid or flexibleas desired.

The composite heater v10 includes an inner elongated strip of woven tapeor mesh 13, having two spaced parallel and desirably .identicalconductive areas 14 and 15 adjacent its two parallel opposite side edges16. Be tween the two conductive areas 16, the tape has a nonconductivearea 17, extending along the entire length of the tape. At one end ofthe heater 10, the two conductive areas 16 are electrically connectedtogether by a bus element 1-8, while at the other end `of unit 10, areas16 are connected respectively to a pair of individual buses 19 and 20,to which the two leads 21 of a power supply cord 22 are connected. Cord22 may have a conventional plug 23 connected to its end, and adapted tobe plugged into a receptacle represented at 24, which receptacle isconnected to a power source represented at 25. The power supplied totheunit by source 25 may typically be l2() v. A.C. The wovenkmesh 13 isconfined between and bonded to a pair of Vlayers 50 of insulativematerial, which eectively 11 or any other part (except for thepreviously mentioned connection to power source The mesh or innerheating element 13 includes a number of elongated strands or wires 26aand 26h made of an electrically conductive material, and forming theelectrically conductive areas 16 of the tape. Also, the woven meshincludes a number of elongated strands 27a and 27b which are woventogether across the entire width of the tape or mesh 13, and which are`formed of a' less conductive and preferably electricallyinsulativematerial. The conductive strands 26a and 2Gb may be formedl of anysuitable material such as a nickel chrome alloy, tungsten alloy,alluminurn alloy, stainless steel, Monel` metal or the like. Theinsulative strands 7.7./.1 and' 27h are in most instances preferablyformed of glass fibers, but may also be formed of Y'asbestos or anyother fibrous material able to withstand the high operating temperatureswith each of the strands 27a and Z719 being formed of a large number ofvery iine glass fibers grouped together to form in essencev a singlestrand. The-strands 26a, 27a and 27h are woven together in anyconventional or suitable weaving pattern, so that the various conductivewires 26a andv 2Gb are interwoven and interloclted with respect to eachother and with respect to the conductive strands 27a a-nd 27h.Preferably, the conductors and non-conductors extend both longitudinallyof the mesh 13 and transversely thereof with the longitudinal conductorsbeing in contactwith the transverse conductors. As will be understood,the non-conductive strands 27a and 27b hold the conductors 26a and 26bin predetermined spaced relationship, `so that hte overall mesh formedby 26a, 26h, 27a and 27h caribe given an accurately predeterminable andcontrolled electrical resistance and heating characteristic.

With more specific reference to the particular weave pattern illustratedin Figs. 1 to 4, `it is noted that in this arrangement thenon-conductive strands designated 27a extend directly longitudinally ofthe woven mesh 13, that is, directly parallel to the opposite side edges16 of the mesh or tape. These longitudinal non-conductive strands arespaced unformly and rather closely across the entire width of mesh 13(that is, between the two opposite side edges 16). The non-conductivestrands designated 27b in Fig. 4 extend directly transversely of strands27a.v and therefore directly transversely of the tape 13. Thesenon-conductors 27h are spaced uniformly and closely along the entirelength of the woven mesh 13, and each of the transverse conductors 27bdesirably extends across the entire width of the mesh, from one of theedges 16 to the other edge 16. Preferably, all of the transverse strands27 of the mesh are portions of a single continuous strand, which firstextends across the tape in one direction, is then doubled back at one ofthe edges 16 (as at 28 in Fig. 4) to extend across the tape in theopposite direction, and then is doubled `back at the opposite edge 16 toreturn again in the first mentioned direction, etc., so that a singlestrand may forrn all of the transverse non-conductors for the entirelength of the tape. As will be apparent, each of the strands 27a or 27bis woven alternately over and then under successive strands extending inthe opposite direction, so that the strands are all effectivelyintegrated into the overall woven tape, as shown in Fig. 3 and 4.

In the Figs. l to 4 arrangement, the conductive strands 26a extendlongitudinally of the tape 13, and parallel to side edges 16, and arespaced uniformly and closely across the width of each of the twoconductive areas 14 and 15. That is, for conductive area 14, the strands26a are provided between the left hand edge 16 in Fig. l, and a line 29which defines the inner edge of conductive area 14. Similarly, forconductive `area 15, the strands 26a are provided at closely spaced anduniformly spaced locations between the right hand edge 16 in Fig. l, andthe inner edge 30 of conductive area 15. These edges 29 and 30 of thetwo conductive areas extend parallel to insulate mesh 13 from parth ione another and parallel to side edges 16 of the tape,

and are spaced apart a substantial distance to provide thenon-conductive central area 17, The width of area 14 is desirably thesame as the width of area `15. Pref-- erably, one of the longitudinalconductors 26a is pro-- vided for each of the longitudinalnon-conductors 27a,l across the widths of the areas 14 and 15, with eachof' the conductors 26a being woven in and out with respect to thetransverse strands in unison with, and along with,

step with the first two strands, that is, when the first twoylongitudinal strands extend upwardly over a particular transversestrand, the second two longitudinal strandsy extend under thattransverse strand, and vice versa.

The transverse conductors 26b of each of the nonconductive areas 14 or15 may comprise portions of a. single elongated wire, which is wovenalternately in op-y posite transverse directions in somewhat the sameman-- ner as has been previously described in connection with transversenon-conductive strands 27h. More specifically, the wire forming thetransverse strands 26b of conductivey area 14 can first extend in onetransverse direction, and then be doubled back at one of the side edges16 (see 31 in Fig. 4), following which the wire extends in the reversetransverse direction to the location of inner edge 29 of the conductivearea, at which location the wire is doubled back (as at 32 in Fig. l) toreturn toward edge 16, etc., for entire length of the tape. As the wire26h extends transversely, it may on each run be woven over and under thelongitudinal strands in unison with an associated one of the transversenon-conductive strands or runs 27b. At each of the points at which oneof the transvers conductors 26b crosses one of the longitudinalconductors 26a, the transverse and longitudinal conductors arepreferably in direct electrical contact so that the conductors of eachof the areas 14 and 15 form together a woven conductive mesh, with thewires of this mesh being held in predetermined relation by theassociated non-conductive strands 27a and 27 b.

Desirably, the total cross sectional area of the longitudinalnon-conductors 27a within each conductive area 14 or 15 is greater thanthe total cross sectional area of the longitudinal conductors 26a inthat same conductive area, and is preferably several times as great. Thesame is also preferably true of the relationship between the crosssectional areas (taken in any longitudinal plane within area 14 or 15)of the transverse non-conductors and conductors. The individual wires26a and 2Gb may be as small as .0002 square inch in cross sectional area(.04 circular mills), and .0005 inch in diameter. Nonconductive strands27a and 27b may have cross sectional area of .0005 to .060 inch (totalcross section of all glass fibers forming one strand). The meshsize ofthe heating element many range between about l0 and 400 of the glassstrands per inch.

The two insulative layers 50 between which conductive mesh 13 is conned,may be formed of any of various materials capable of providing suitableprotection to the heater unit against electrical contact with nearbyparts. Suitable and preferred insulating materials may be selected fromthe general class of plastics, elastomeric or non-elastomeric, includingsuch thermosetting resins as the phenol formaldehyde, urea formaldehyde,melamine modified phenol formaldehyde or urea formaldehyde, epoxide,polyester and polysiloxane resins, and such elastomers as the heatresistant silicone rubbers and neoprene. The properties and particularlythe thermal resistance of all such plastics being known, it is but amatter of selecting among them one or a combination of materialsHowever, the in and out weaving of' the second ltwo longitudinal strandsis of course out of' assegna capable of retaining such properties aschemical Vor body stability, dimensional stability, and iiexibility ifdesired, under the. temperature conditions to which the insulation maybe subjected by the mesh heating element 13.

I prefer to reinforce either or both insulating layers 50 by the use ofwoven fabric such as Woven glass. In practice the insulating layers 50may be formed by impregnating the fabric with any ofthe above mentionedplastics and laminating type resinous materials, and then applying theimpregnated fabric and the plastic material to opposite sides of element13 prior to curing. The reinforcing fabric may be impregnated with theappropriate laminating plastic by any of various possible methods, suchas spraying a solvent solution of the resin (either catalyzed oruncatalyzed, depending upon the resins used) onto one or both sides ofthe fabric, or by dipping the fabric in the resin and then suspendingthe fabric vertically to drain off excess resin, or by'knife coatingthefabric with the resin at an appropriate and uniform thickness. Any'suchmethods may be used to produce impregnated fabricswhich may be air driedor forced hot air dried for an appropriate time to evaporate anysolvents or to partially set the resins prior to a iinal cure which mayoccur during -the laminating process. After drying, the fabric maybestored for subsequent use in the manufacture of thelaminated heatingunit. If desired, each of the insulative layers 50 may include more thanone of the sheets of plastic impregnated reinforcing fabric, in order toincrease the overall strength of the composite unit.

The three terminals or bus elements 18, 19 and 20 may be Iformed ofconventional metal screen or mesh, made up entirely of conductive` metalwires Woven together to produce a mesh which has considerably greaterelectrical conductivity and less resistance than the heater mesh 13. Thebuses 18, 19 and 20 may be formed of any of the same conductive metalswhich may be utilized as the conductors 26a and 26b in heating element13, but the wires of screens 18, 19 ,and 20 are Ydesirably considerablylarger in diameter `than conductors 26a and 26h, and are desirablyconsiderably closer together than the conductors V26a and 26b`of heater13. The mesh size of screens 18, 19 and 20 may typically range betweenabout 30 and 400 per inch'. The twoscreens 19 and 20lie across the upperVsides of iirst'ends of conductive areas 14 and 15, between the mesh'and the upper insulative layer 26, and are in direct electrical contactwith the conductors 26a and 26h of element 13 `for conductingelectricity thereto. Screen 18 is similar but extends across the entirewidth of the woven tape, to form an electrical connection between secondends of the two areas 114 and 15. Preferably, the screens, 18, 19 and 20are soldered to conductors 26a and 2Gb prior to the bonding together ofthe insulative layers 26. Also, the wire leads are soldered to the twobuses 19v and 20', so that current will ow from one of these buses alonga iirst of the conductive areas 14 and 15, then across the bus 18, andthen back along the second conductive area. Before layers 50 are placedabout the inner heater parts, an uncured resin may be applied as at 131about the buses 18, 19 and 20 and associated portions of the mesh 13, tocompletely encapsulate and protect the terminal areas. This resin may beof the same composition as that used in layers 50, and maybe cured atthe same time as those layers. Preferably, layers 50 have peripheraledge portions at 32 extending laterally beyond the tape and terminals atall points, to form a continuous peripheral area at which layers 50 aredirectly bonded together.

Alfter theparts 13, 26, 18, 19, 20' and 131 have all been assembled inthe relation illustrated in Figs. l and 2, these parts may be heatedunder pressure to a temperature capable of curing the resin, or othercurable or hardenable material contained in layers 50 and regions 131,to bond these, layers 50 tightly together and to the intermediate heaterelement 13 and bus assemblies. This bonding together of the laminates orlayers may be accomplished by means of a heated hydraulic press, f orexample of the type used'in the making of plywood. This press maytypically be adapted to compress the various layers together at apressure that may be upwards of 500 pounds per square inch, and which issufficient to compact the layers to very thin hard form. During suchcompression, the resin or other curable material is heated at anappropriate curing temperature, say upwards of 350 Fahrenheit, over asuitable period of time, typically 15 minutes, to thermally polymerizeor set the resin to form a composition that will remain dimensionallystable and resistant to the heat which the element is designed tc`generate.

If desired, the laminating process may be performed by means of theknown vacuum bag technique, in which the various layers to be bonded areplaced in a plastic, rubber or metal foil bag from which the air isevacuated. The evacuated bag is then placed in a controlled ternperatureoyen to cure the resins and form the laminating bonds at reducedpressure. This method may be utilized to fasten flexible laminatedheating elements onto parts requiring heating of the layers in deformedor non-planar shapes which can not be formed practically by hydraulicpress lamination.

As will be apparent, the pressure curing of the resin in layers 50 andregions 131 will force that resin into the interstices or aperturesformed between the strands 26a, 2611, 27a, and 27b of heater element 13,to tightly bond the resin to the strip 13, while the two layers 50 arebeing correspondingly bonded tightly together about the periphery ofelement 13, and are being bonded to the buses at the ends of element 13.

It is contemplated that where the carrier part 11 is of a typepermitting bonding of the heater unit 10 directly thereto duringformation of the heater unit, such direct bonding will be effected byplacing the part 11 in the hydraulic press or other laminating equipmenttogether with the parts 13, `26, etc. Aof unit 10. The laminatingprocess then cures the resin Aofthe under layer 50 while it is directlyin contact with part 11, to tightly bond the resin and unit 10 to partA11 over the entire area of unit 10.

Figs. 5 and 6 illustrate another f orm of the invention which may beidentical with that of Figs. 1 to 4 except for the arrangement of theconductors in woven mesh 113, and the formation of the bus elements 118,119 and 120. Speciiically, the mesh 113 includes longitudinal conductors126:1, correspondingto those shown at 26a in Figs. 1 to 4, but does notinclude transverse conductors such as those shown at 26b in Figs. 1 to4. The arrangement of the glass strands, .insulative layers 150,encapsulating resin 231, and power leads y121 may all be substantiallythe same in Figs. 5 and 6 as in the rst form of the invention.

In Figs. 5 and 6, the bus elements 118, 1'19 and 120 may be thin sheetmetal shim stock, of copper, stainless steel, or the like, with thisshim stock being doubled to the Fig. 6 U-shaped configuration, toelectrically engage both sides of tape 113. Preferably, the shim stockis precoated with solder, and after being deformed to the Fig. 7condition, is heated to melt the solder, while part 118, 119 or 120 istightly clamped against the tape, to thus form a conductive solderconnection between the bus elements and the conductors of tape 113. Theencapsulating resin 231, and the insulative outer layers 150, are thenapplied in the same manner as in Figs. l-4.

Fig. 7 is similar to Fig. 4, but illustrates fragmentarily the wovenmesh portion of another form of the invention. This third form isidentical with that of Figs. 1-4, except for the'deletion of thelongitudinally extending conduc tors 26a` of Figs. 1 4. That is, themesh 213 of Fig. 7 has only transverse conductors (226b),- correspondingto conductors 2Gb of Figs. l-4. A s in the rst form of the invention,all Vof these transverse conductors (in each of the two conductiveareas) are` portions of a single wire which is woven back and forth asin Fig. 4, and whose ends are in electrical contact with the buselements (see bus 218 in Fig. 7). Thus, current flowing through theheater of Fig. 7 must follow a very circuitous back and forth path, togive to the element a very high electrical resistance.

In all of the forms of the invention, the total overall thickness of theunit 10, including mesh 13, 113 .or Z13, and layers 50, 150 or 250 (butnot taken at the locations of buses 18, 19, 20, etc.) may typically bebetween about .015 inch and 1A of an inch. The insulative layers 50, 150and '250 may typically be between about .001 inch and 1A; of an inch.The number of longitudinal conductors present in each form of theinvention is preferably between about and 100 per inch, and the numberof transverse conductors is preferably between about 0 and 50 per inch.In the case of both the longitudinal and transverse conductors, fit maybe desirable in some cases 4to provide conductors at only alternatenon-conductive bers, or at every -second or third non-conductor, or evenless frequently where necessary to achieve a desired overall result.

In using any of the three forms of heater, the user merely connects plug23 into power socket 2.4, so that current flows through the conductiveareas 14 and 15 in opposite directions, to produce heat. The overallresistance of these areas is such as to develop a desired amount of heatat a particular predetermined operating voltage. Since the two powerleads 21 (or 121) are connected to the same end of unit (or 110), theunit may be very long if desired, and may be applied to a carrier partof virtually any shape. For instance, if the part 11 is left olf of theFig. 1 arrangement, and the resin and other parts are chosen to give thetape flexibility, the heater unit may be wrapped as a long tape about apipe, or may be wrapped about a work piece of virtually any other shape.This would not be as easily attained if the two leads 21 came out ofopposite ends of the elongated tape like unit.

As an example of a particular unit made in accordance with the presentinvention, a steel plate of approximately .050 inch in thickness wasdegreased and sandblasted to provide surface irregularization. Twolayers of approximately 60 mesh close weave glass cloth impregnated withphenolic resin were then laid on the steel plate, over which was applieda mesh heating element such as that shown at 13 in Figs. 1-4. The heator strip had one conductor 26a-or 26b for each principal glass strand27a or 27b, and had approximately 40 of each per linear inch. Eachprincipal glass strand 27a or 27b included a large number of glass bers.The cross sectional area of the longitudinal glass ibers was about 20times as great as the cross sectional area of the longitudinalconductors 26a, and the same was true of the transverse glass andconductive strands. The 'conductors 26a and 26h used in the example hada diameter of about .002 inch, and were formed of constantan while the`composite cross sectional area of all of the glass fibers in eachstrand 27a or 27b was about .000006 square inch.

Over the strip 13, there was applied another layer of theresin-impregnated glass cloth, with terminal screens of 400 mesh Monelmetal `being positioned as shown at 18, `19 and 20 in Fig. l, and 'beingsoldered to the conductors of the heater strip 13, and encapsulated inphenolic resin as at 131. All of these layer and the base plate werethen covered on both sides with double thicknesses of uniformly texturediblotter paper and placed in a hydraulic press whose flat platens wereheated to 350 F. and which were then closed upon the layers at apressure of approximately 500 p.s.i. for approximately minutes.

As a second example, the foregoing procedure was employed using, inplace of the impregnating and encapsulating resin mentioned before, aphenolic-epoxide resin sold by Narmco Resins and Coatings Co. as Conolon506. Also, the. heater strip 13 was preimpregnated with uncurde Conolon506 resin prior to the lamination process, to assure thorough bonding ofthe strip 13 to the other parts. The fabric utilized in this example-was formed of glass iibers and conductive strands of substantially thesame sizes, mesh, etc. as in the irst example, except that no transverseconductors 26b were used (see Figs. 5 and 6). The bus terminals weremade as shown in Figs. 5 and 6.

A third example was made using as the insulating layers a silicone resinimpregnated onto a glass fabric. The heating unit was a common weave asshown in' Fig. 4, but included one of the conductors 26a or `2Gb (.002inch diameter) for every third principal glass strand 27a or 27b (inareas 14 and 15). The heater strip was pre-treated with Dupont Volan toenhance the adhesion of the resin to the glass fibers. This unit was notapplied over a rigid backing plate, but was laminated in such a mannerthat it produced a free standing and flexible unit which wassubsequently bent to fit-over a part of non-planar shape, and wassecured thereto.

Any of the described laminations, after being bonded as described, mayIbe coated with an insulating varnish that favors preservations andprotection of the product, and enhances its appearance.

I claim:

1. An electrical heating element comprising an elongated thinelectrically conductive woven mesh tape composed of elongated strands ofmaterial extending in at least two different directions and each closelyinterwoven in a predetermined pattern with a series of the otherstrands, some of said strands of material being electrically conductiveand offering sufficient resistance to develop heat upon passage ofelectricity therethrough, said conductive strands being arranged to formtwo conductive areas extending longitudinally of the tape and spacedlaterally apart and insulated from one another for an extended distance,others of said strands being relatively non-conductive of electricityand being interwoven with said `conductive strands and forming anonconductive area elongated longitudinally of the tape and locatedlaterally between said two conductive areas said conductive strandsincluding wires running continuously back and forth transversely of andat opposite sidse of said non-conductive area.

2. An electrical heating element as recited in claim l, including meansfor connecting two sides of an electric power source to said twoconductive areas respectively at a first location along the tape, andcross connecting means for electrically connecting said two conductiveareas together at a second location along the tape spaced longitudinallyof the tape from said first location and so that current from saidsource -will flow in a first direction longitudinally of the tape alongone of said conductive areas and then through said cross connectingmeans to tlow back along the other conductive area in the secondlongitudinal direction for return to said source.

3. Anelectrical heating element as recited in claim l, including a layerof non-conductive insulating material bonded to and insulating at leastone side of said woven mesh tape.

4. An electrical heating element as recited in claim l, in which some ofsaid conductive strands extend longitudinally of the tape and areinterwoven with a series of the non-conductive strands extendingtransversely of the tape.

5. An electrical heating element as recited in claim l, in which saidconductive strands extend both longitudinally and transversely of thetape and are interwoven with one another and with the non-conductivestrands along said two conductive areas, but are discontinued at saidintermediate non-conductive area, said non-conductive strands extendingboth longitudinally and transf 9 versely of the tape throughout bothsaid conductive areas and said intermediate non-conductive areas.

6. An electrical heating element comprising an elongated thinelectrically conductive woven mesh tape composed of elongated strands ofmaterial extending in at least two different directions and each closelyinterwoven in a predetermined pattern with a series of the otherstrands, some of said strands of material vbeing electrically conductiveand offering suflicient resistance to develop heat upon passage ofelectricity therethrough, said conductive strands being arranged to formtwo conductive areas extending longitudinally of the tape and spacedlaterally apart and insulated from one another for an extended distance,others of said strands being relatively non-conductive of electricityand being interwoven with said conductive strands and-forming anon-conductive area elongated longitudinally of the tape and locatedlaterally between said two conductive areas, said conductive strandsincluding wires running back and forth transversely of and at oppositesides of said non-conductive area, rst connector means for connectingtwo sides of an electric power source to said two conductive areasrespectively at a Ifirst location along the tape, cross connecting meansfor electrically connecting said two conductive areas together at asecond location along said tape spaced longitudinally of the tape fromsaid rst location and so that current from said source will ow in a. rstdirection longitudinally of the tape along one of said conductive areasand then through said cross connecting means to flow back along theother conductive area in the second longitudinal direction for return tosaid source, and two layers of non-conductive insulating material bondedto and insulating the opposite sides of said woven mesh tape.

7. An electrical heating element as recited in claim 6, in which saidIfirst connector means and said cross connecting means are 4busescontacting said conductive strands and `confined between the tape andsaid nonconductive layers.

8. An electrical heating element as recited in claim 6, in which some ofsaid conductive strands extend longitudinally of the tape and areinterwoven with said wires running transversely of and at opposite sidesof said non-conductive area.

9. An electrical heating element as recited in claim 6, in which saidconductive strands extend both longitudinally and transversely of lthetape and are inter-woven with one another and with the non-conductivestrands along said two conductive areas, but are discontinued at saidintermediate non-conductive area, said non-conductive strands extendingboth longitudinally and transversely of the tape throughout both saidconductive areas and said intermediate non-conductive areas.

References Cited in the file of this patent UNITED STATES PATENTS1,615,294 Turver Ian. 25, 1927 2,345,300 Simpson et al. Mar. 28, 19442,496,279 Ely et al. Feb. 7, 1950 2,503,457 Speir et al. Apr. l1, 19502,511,540 Osterheld June 13, 1950 2,522,542 Schaefer Sept. 19, 19502,533,409 Tice Dec. 12, 1950 2,643,320 Pfenninger June 23, 19532,719,907 Combs Oct. 4, 1955 2,759,092 Fortin Aug. 14, 1956 2,817,737Morris Dec. 24, 1957

